1. Field of the Invention
The instant disclosure relates to a power on reset circuit, a power on reset method and an electric device using the same; in particular, to a power on reset circuit that can be shut down or turned on automatically, and its corresponding power on reset method and an electric device using the same.
2. Description of Related Art
As known, the power on reset circuit is usually used to detect the rising and falling of the voltage of a power supply for an electric device. In conjunction with FIG. 1A and FIG. 1B, FIG. 1A shows a schematic diagram of a traditional power on reset circuit, and FIG. 1B shows a schematic diagram representing the output voltage of the traditional power on reset circuit shown in FIG. 1A. As shown in FIG. 1A and FIG. 1B, the power on reset circuit 1 has a rising threshold voltage VTH_R and a falling threshold voltage VTH_F. As the power supply starts to provide power to the electric device butt the voltage of the power supply has not yet reached to the rising threshold voltage VTH_R, the power on reset circuit 1 starts to detect the voltage of the power supply VDD and outputs an output signal VOUT at low level, which represents that the entire circuit of the electric device is in its reset status. As the voltage of the power supply VDD reaches to the rising threshold voltage VTH_R, the power on reset circuit 1 outputs an output signal VOUT at high level, which represents that the electric device has been turned on; however, the power on reset circuit 1 continually detects the voltage of the power supply VDD. After a period of time, as the voltage of the power supply VDD falls to be less than the falling threshold voltage VTH_F, an output signal VOUT output by the power on reset circuit 1 turns to be at low level, which represents that the entire circuit of the electric device has returned to it reset status.
However, after the voltage of the power supply becomes stable and the electric device is turned on, the power on reset circuit 1 shown by FIG. 1A and FIG. 1B would continually detect the voltage of the power supply VDD, which thus results in the unnecessary power consumption.